Making hair go straight up instead of following the shape?
Enable Advanced and Rotation, then set the Initial Orientation to Global Z:



Note that you'll have to rotate your objects so they are facing either the +X or +Y direction instead of the +Z direction. See Why are the objects in my hair particle system not sitting on top of the ground?.

By using this technique the orientation of the particles is kept independent of their size, and you can add some random rotations via the Particle settings > Rotation > Random settings:



Adding such randomizations will help make repeated use of the same models less noticeable.